Electrical discharge device



April 25, 1939. J. E. BEGGS ELECTRICAL DISCHARGE DEVICE Filed D60. 17, 1956 Figl.

Aux. Anode Current Main Anode Current Inventor: James E. Be gs,

. His Attorney.

Patented Apr. 25, 1939 ELECTRICAL DISCHARGE DEVICE James E. Begs Schenectady, N. Y., assignor to General Electric Company, a corporation oi New York Application December 17, 1936, Serial No. 116,397

4 Claims.

The present inventionrelates to electrical discharge devices, and more particularly to thermionic vacuum tubes such as are employed in the radio art.

It is an object of the invention to provide a vacuum discharge device by means of which a single input voltage may be caused to produce a plurality of independent output voltages whose relative magnitudes are variable in accordance with variations in an electrical condition. In one application of the invention this is accomplished by employing; in addition to the usual electrodes, an auxiliary anode and a secondary control grid so arranged as to divert varying amounts of current from the main to the auxiliary anode in response to changes in the bias applied to such secondary grid.

The features of novelty which I desire to protect herein will be pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof will best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 is a longitudinal section of a discharge device suitably embodying the invention; Fig. 2 is a view corresponding to a cross-section of the device shown in Fig. 1; Figs. 3 and 4 are graphical representations useful in explaining the operation of the invention, and Fig. 5 shows a particular application illustrating the utility of the invention.

structurally the discharge device shown in Fig. 1 comprises a thermionic cathode ill, a main anode II,. a plurality of successively arranged grids interposed between the anode and cathode,

such grids being numbered l2 to l5 inclusive,

and an auxiliary anode comprising electrically connected conducting rods l1 and i8. These various electrodes, except for the anode II, are supported and maintained in proper alinement by means of a pair of insulating disks 20 and 2| adapted to receive and retain the ends of the supporting elements for the electrodes. The constructional details of the individual parts may be briefly enumerated as follows:

The cathode It), as illustrated, is of the indirectly heated type conventionally employed in vacuum discharge devices and may comprise, for example, a nickel cylinder coated externally with a highly electron emissive material. Within the cathode there may be arranged an electrical resistance heater adapted to raise the cathode temperature to a point of thermionic emission. The main anode I I is shown as comprising a metallic cylinder substantially concentrically surrounding I the cathode and having a suflicient area so that its heat dissipating capacity is relatively great. The various grid electrodes, which are shown only in part for the sake of clarity, may comprise 5 sinuously wound fine metal wires supported on conducting rods which in turn are retained by the disks 20' and 2|. The auxiliary anode parts i! and I8 have been already referred to.

The electrode structure as so far described is enclosed in an evacuated metal envelope comprising a generally cylindrical portion 24 closed at its lower portion by a flanged header 25 welded or otherwise hermetically joined thereto. The header 25 is provided with a plurality of insulated lead-in connections by means of which the various enclosed electrodes may be energized at desired potentials. .Thus, in the arrangement illustrated the auxiliary anode members I! and iii are connected to a common lead-in conductor 21 which is sealed through a glass element 28 hermetically fused into a metallic thimble 29. A similar seal and lead-in connection is illustrated for the anode II with which is connected the lead-in conductor 3|. The connections for the remaining electrodes are indicated somewhat incompletely because of the plane in which the illustrated section is taken, but it will be understood that they are of generally similar nature to those already described." For reasons which will be explained more fully in the following, the lead-in connection for the grid l2, which is the main control grid, is made at the opposite end of the enclosing envelope. This connection is shown as being made through a lead-in conductor 34 which connects with a metal cap or contact 35 supported from the main envelope by means of aninsulating disk 31.

For purposes of convenient mounting the bottom of the flanged header 25 is cldsed by means of an insulating cover or plate 38 formed, for example, of a phenolic coiidensation product. This cover is provided centrally with a hollow projecting portion 40 adapted to receive a metal tubulation 4! which serves as a seal-01f conduit for the evacuation of the metal envelope. Also supported by the cover member 40 there are provided a number of projecting contact studs 01' which two, numbered 43 and 44, are illustrated. These studs are connected to the various lead-in conductors for the enclosed electrodes and comprise means for securing the tube as a whole in a cooperating socket formed, for example, in a composite panel comprising sections 46 and 41. These panels are provided with stud-receiving I.

2. parts 49 and 48 which are connected with fixed conductors I and The functional aspects of my novel discharge device may best be understood by reference to Fig. 2. In this figure the cathode ill, the anode H and the inner grid i2 (formed elliptically because of spacing requirements) comprise the elements of a triode discharge device in which the grid II is operable as a control electrode. In addition to these elements, however, the invention provides an auxiliary anode comprising rodlike conducting members I1 and I8 and a second control grid I4 interposed between the auxiliary anode and the main anode. The position of the auxiliary anode (as exemplified by the rods 11 and II) is such as to beoutside the principal discharge path to the main anode. This is accomplished in the particular arrangement shown by placing the rods i1 and I! in the plane which contains the supporting elements for the various grid members.

Disregarding for the moment the grids l8 and II (these being primarily useful as screen grids) the operation of the device may be described as follows, it being assumed that the main and auxiliary anodes are maintained at a positive potential with respect to the cathode. With no potential, or an extremely low potential, 'impressed on the grid ll, substantially all of the current proceeding from the cathode will be drawn to the main anode II with only a very small portion, if any, going to the auxiliary anode.

However, if a potential in the nature of a negative bias is' now impressed on the grid I4, a certain percentage of the main discharge current willbe retarded and diverted by this electrode so as to be received by the auxiliary anode. The amount so diverted will increase in proportion to the magnitude of the bias and with very high values of bias may comprise substantially the entire discharge current. I A decrease produced in this manner in the current flowing to the main anode Ii will necessarily involve a corresponding decrease in the magnitude of the output current variations which can be producedby the input voltage applied to the control grid l2. Since the relation between these'two quantities is by definition the amplification factor of the electrode combination comprising the cathode It, the anode II, and the control grid 12, it will be seen that this factor decreases with an increase in the bias impressed on the grid ll.

Furthermore, as the amplification factor of the main anode decreases as a result of increasing the bias of the grid it, the amplification factor of the auxiliary anode must increase in approximately inverse ratio in accordance with the increasing amounts of current being diverted to it. These eflects are both illustrated in Figs. 8 and 4, which show respectively the variations of main anode current and auxiliary anode current with the input voltage for various values of bias (Gs) impressed on the auxiliary grid. Thus, for. zero bias the relationship between the main anode current and the input current is represented by a curve of relatively steep slope, whereas the corresponding curve for the auxiliary anode is of relatively small slope. Conversely for a higher negative biasing potential of, say, 6 volts the relation between the main and auxiliary anode amplification curves is approximately reversed.

1 coil 59 a current which a discharge device corresponding to that described in the foregoing is used to accomplish the dual functions of automatic selectivity and volume control. In this circuit an antenna 52, a radio frequency amplifier 53, a local oscillator and converter M, a detector 55, an audio frequency amplifier B6 and a loud speaker 51 are indicated symbolically whereas an intermediate frequency amplifier including a discharge device of the type under consideration is shown in greater detail. For purposes of convenient identification, parts corresponding to those already described are similarly numbered.

. The-cathode is shown as being connected to ground by means of a self-biasing resistor ts. Input potential is applied to the control grid II by means of a pair of tuned coupled circuits fed by the output of the'converteril. These circuits comprise. coupled transformer windings is and 60 and associated variable condensers" and 62. It is known in connection with the operation of a circuit of this type that for very low signal strengths relatively high selectivity is de sirable in order to prevent interference while a higher values of signal strength selectivity may advantageously be decreasedv in order to enhance fidelity-of reproduction. It is also known that adjustment of selectivity may be accomplished by varying the coupling of the coils I59 and 60 within certain limits. In my copending application, Serial No. 106,97'L'filed October 22, 1936, I have shown that appropriate changes in eflective coil coupling may be accomplished automatically by supplying to the tuned circuit which contains the is 90 degrees out of phase with the input voltage applied to the grid l2 and which is variable in magnitude with the incoming signaLstrength. In the circuit illustrated in Fig. 5 hereof this is accomplished by afeed-back connection from the auxiliary anode, which is shown as a single element but which corresponds to the parts i1 and I8 described in connection with Iilgs. l and 2. The feed-back connection includes a phase-shifting circuit comprising a condenser 64, a resistor 65 and a blocking condenser 88.

By impressing on the second or auxiliary control grid M a negative biasing voltage which is proportional to the signal strength it is possible to vary the amount of feed-back in the requisite manner. Thus, an increase or a decrease in the bias supplied to the electrode ll will result in a corresponding variation in the current flowing to the anode II. This in turn will modify the selectivity of the circuit by varying the efi'ective coupling of the coils 59 and 80 in accordance with the principles already explained.

In addition to the selectivity control operation explained in the foregoing, further features of my invention make it possible for automatic volume control to be accomplished by the same discharge device and biasing potential which produce the selectivity control. This is a result of the previously mentioned fact that the action of the grid 14 in increasing the current to the auxiliary anode simultaneously decreases that to the main anode ll. Consequently a decrease in selectivity as a consequence of a rise in signal strength is accompanied by a greater degree of volume regulation on the part of the grid ll.

In order to prevent undesired feed-back from the main anode to the auxiliary anode or to the control grid 12, it is advantageous to provide shielding between them. Such shielding may be accomplished, for example, by means of a conventionalscreen grid l5 positioned adjacent the main anode and adapted to be maintained at a relatively fixed potential with respect to it. Similarly, feed-back from the auxiliary anode to the main control grid l2 may be prevented by use of a further screen grid l3 interposed between them. The shielding may be made more complete by an arrangement of the tube parts such as that illustrated in Fig. 1 in which means in the form of a metallic shield H is provided between the anode lead-in connection 3| and the remaining conductors in the tube. This shielding may be further extended by means of a similar metallic shield 12 in the tube base and a shielding baflle 13 provided in connection with the panel on which the tube is mounted. The lead-in conductor 34 for the control grid I 2 is effectively separated and shielded from the other lead-in connections by being brought out the opposite end of the envelope as previously explained. With this arrangement the entire envelope of the discharge may serve as a shielding means for the conductor 34. In operation the envelope is preferably connected to ground as, for example, by a connection 15 brought out through the base of the tube.

Numerous applications of the invention may be made in addition to that described in the foregoing. For example, by applying signal input to the second control grid and a fixed'bias to the first control grid, eflective push-pull operation may be obtained as a result of the simultaneous but inverse variations'oi the currents to the main and auxiliary anodes. Furthermore, while I have shown a particular structural embodiment, it will be understood by those skilled in the art that many modifications may be made without departing from the invention, and I aim by the appended claims to cover all such modifications as fall within the true spirit and scope of the foregoing disclosure. The system of combined selectivity and automatic volume control described herein is not a part of the present invention but is fully described and claimed in my application, Serial No. 106,977, filed October 22, 1936, and assigned to the same assignee as the present invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electrical discharge device including a cathode and a main anode, a first control electrode, an auxiliary anode and a second control electrode arranged between the cathode and main anode in the order named, and means for shielding said anodes from each other and from said first control electrode while leaving the auxiliary anode exposed to the second control electrode.

2. In an electrical discharge device including a cathode and a main anode surrounding the cathode, a first and second control grids interposed between the cathode and main anode in the order named, a series of supporting rods for said grids arranged substantially in a single plane, an auxiliary anode comprising conducting members arranged in said plane between the first and second control grids, and means including a pair of screen grids arranged to shield said anodes from one another and from said first control grid while leaving the auxiliary anode directly exposed to the second control grid.

3. In an electrical discharge device including a cathode and a main anode, a first control grid and an auxiliary anode interposed between the cathode and anode in the order named, said auxiliary anode being positioned outside the principal discharge path to the main anode, a second control grid between the auxiliary and main anodes efiective during operation of the device to vary the relative amplification levels of said anodes in accordance with variations in the potential impressed on said second grid, and a pair of screen grids respectively interposed between the first control grid and the auxiliary anode and between the auxiliary anode and the main anode.

4. An electrical discharge device comprising an evacuated envelope enclosing a cathode and a main anode surrounding the same, a first control'grid, an auxiliary anode, and a second control grid interposed between the cathode and anode in the order named, said auxiliary anode being positioned out of the principal discharge path between the cathode and main anode, a screen grid between the first control grid and the auxiliary anode, and another screen grid between the second control grid and the main anode, the auxiliary anode being directly exposed to the second control grid.

JAMES E. BEGGS. 

